FR2641404A1 - Solution for dissolving metal compounds containing dibutylphosphate ions and process of decontamination using this solution - Google Patents

Abstract

The invention concerns a solution for dissolving metal compounds containing dibutylphosphate ions and a process of decontamination using this solution. This solution comprises a diamide such as a tetralkylmalonamide, for example N,N'-dimethyl-N,N'-dibutylpropanediamide, an organic diluent, for example butyric acid, and an inorganic acid such as nitric acid. These solutions may be used to decontaminate apparatuses soiled by compounds of Fe III, of actinides and of rare earths in the III state.

Description

264 1404

  Solution for dissolving metal compounds

  dibutylphosphate ions and decontamination process

mination using this solution.

  The subject of the present invention is a solution for dissolving metal compounds containing dibutylphosphate ions (DBP) and a process for decontaminating apparatus using

this solution.

  Metal compounds containing

  DBP ions are formed especially in instal-

  irradiated nuclear fuel reprocessing lations using tributyl phosphate (TBP)

  as an extractant for uranium and plutonium.

  In fact, in these installations, tributyl phosphate degrades, in particular under the action of radiation, and the main degradation product is dibutylphosphoric acid (DBP) which forms, with most metal ions, sparingly soluble compounds in organic phases

  and aqueous, depositing on the apparatus.

  Also, in these installations, it is necessary to remove the solid compounds thus deposited, and this can be done by washing the apparatuses using a solution of hot sodium hydroxide.

and concentrated.

  However, the use of such a solution

  tion leads to the production of radioactive waste

  not incinerated, which presents certain disadvantages

nients.

  Also, research has been done to find other solutions capable of dissolving

  metal compounds containing dibutyL- ions

  phosphate, which can be destroyed by incineration-

  tion in order to avoid the production of quantities

  significant amounts of radioactive waste.

  The present invention has precisely for

  object a solution for dissolving metal compounds

  ques containing dibutylphosphate ions, which overcomes this drawback. This solution includes a diamide,

  an organic diluent and an inorganic acid.

  The diamides used can be in particular tetraalkylmalonamides such as those corresponding to the formula:

R1 R1

R2- N-CO-CH2-CO-N R 2

  in which R1 and R2 which may be the same or different, are alkyl radicals having

  preferably 1 to 8 carbon atoms.

  As an example of such tetra-alkylmalona-

  mides, there may be mentioned N, N'-dibutyl-N, N'-dimé

  thyl-propanediamide. These tetra-alkylmalonamides can be obtained by reaction of the chloride of malonic acid with the corresponding secondary amine in the presence of triethylamine according to the following reaction scheme: R1 NH + CL R l \ RIR1

  R2 / NH + C1 COCH2COCI-, R N-CO-CH2-CO-N R2

(C2H5) 3N

  According to the invention, one can use as tetra-alkylmalonamide one of these isomers or

mixtures of these.

  The secondary amines used as starting material for the synthesis of the tetra-alkylmalonamides of the invention can be prepared by reaction of the appropriate bromide on the appropriate amine according to the following reaction scheme: R1

3R5Br + R2-N H2 N + BrH-2 RNH + KBr + H20.

R2 R2 '

  The diluents used in the solution

  of the invention are organic products, incinerated

  bles, which are preferably miscible with water although it is also possible to use diluents miscible with organic solvents such as hydrocarbons used as diluent in plants for reprocessing irradiated nuclear fuels. The diluents used in the invention preferably have a relatively high flash point, for example of

45 to 1200C.

  Examples of water-miscible diluents that can be used include organic acids such as propionic acid and butyric acid, which have flash points of 51 C and 76 C respectively. The diluent can also be an alcohol like octanol-2 which has a point

  71 C flash, or an amide such as dialkylaceous N, N-

  tamides and the N, N dialkylformamides, for example N, N-diethylacetamide which has a flash point of 70OC and the N, N-dibutylformamide which has a point

100 C flash.

  Preferably used as a diluent

butyric acid.

  The inorganic acid used in the solution of the invention is an acid whose anion in the presence of diamide is capable of displacing the DBP ions of the metal compound to be dissolved. It is possible, for example, to use hydrochloric acid or preferably

nitric acid.

  With the solution of the invention, a metal ion Mn + is displaced from its complex M (DBP) n, by transforming it into a complex M (X) n (L) X soluble o

  L is a neutral extractant consisting of tetra-al-

  kylmalonamide and X an anion such as N03-. We then have the following solubilization reactions: M (DBP) n + nHNO3 + xL- M (NO3) nLx + nHDBP or M (DBP) n + mHNO3 + xL> M (NO3) m (DBP) nmLx + mHDBP with m < not

  According to the invention, we thus replace before-

  soda with a completely incinerated solvent

  maple whose use does not interfere with operations

  which will follow the cleaning of the equipment.

  Indeed, this solvent does not require new installations and fits easily into the processes of current factories because it can be eliminated by the exits of already existing effluents which accept either aqueous solutions, or organic solutions whose incineration produces

small amounts of ash.

  The use of a diamide such as a tetra-

  alkylmal-onamide and an organic diluent allows the evacuation of the solutions after use to the effluent treatments. It is also possible to then rinse the devices with water or an organic solvent and thus avoid any risk of mixing with the usual extractant, ie

tributylphosphate.

  According to the invention, the concentrations of diamide and of inorganic acid are chosen as a function of the metal compound to be dissolved and

the nature of the diluent used.

  When the butyric acid is used as diluent, the concentration of diamide, for example of tetraalkylmalonamide in the solution may vary

  0.1 to 1, Smol / l and the concentration of inorganic acid

  nique, for example in nitric acid, can vary

from 0.1 to 4 mol / l.

  The solutions of the invention are suitable for dissolving numerous metal compounds containing DBP ions. Examples of such compounds include the compounds of Pu (IV), U (VI), La (III), Fe (III), Zr (IV), Th (IV), soils

rare in state (III) and U (IV).

  The solutions of the invention can be used in particular for decontamination

  of equipment soiled by precipitates of compound

  its metals containing dibutylphosphate ions.

  Also, the invention also relates to a process for decontaminating these devices, which consists in rinsing the devices using a solution according to the invention, comprising

  a diamide, for example N, N'-dibutyl-N, N'-dimethyl-

  propanediamide, an inorganic acid such as nitric acid and an organic diluent such as butyric acid. When this solution is used to decontaminate an apparatus, the apparatus can then be rinsed with nitric acid or with an organic diluent which may for example be an aliphatic hydrocarbon or a mixture of aliphatic hydrocarbons such as the products sold under

  the names of hydrogenated tetrapropylene (TPH) or Hyfrane.

  In both cases the solutions used

  for decontamination can be incinerated.

  Other characteristics and advantages of the invention will appear better on reading the

  following examples, given of course by way of illustration

trative and not limiting.

  In all the examples which follow, N, N'-dimethyl-N, N'dibutylmalonamide is used

  (DMDBMA) which is prepared as follows.

  1 mole of N-methyl-N-butylamine and 1 mole of triethylamine are dissolved in 300 mt of methylene chloride. Cool to tO C, then gradually add 0.5 mole of malonyl chloride in 150 ml of methylene chloride to the reaction medium. The addition is carried out slowly because the reaction is strongly exothermic. After this addition,

  the reaction medium is allowed to return to temperature

  ambient temperature and stirred for two hours.

  Then washed several times with water to remove the hydrochloride and once with a 10% sodium carbonate solution to remove the residual acid and again with water. It is dried, then the solvent is removed, the desired product distills at 140-144 C under 0.3mm Hg, with a yield

45%.

  The product is then recrystallized from hexane and white crystals are thus obtained.

having a melting point of 52 C.

Examples 1 to 3.

  In these examples, solutions in accordance with the invention are used to dissolve precipitates of Fe (DBP) 3. These solutions consist of butyric acid, N, N'-dibutyl-N, N'-dimethyl-malonamide

  (DMDBMA) and nitric acid, and they have concentrations

  different trations in nitric acid and DMDBMA.

  In all the examples, the operation is carried out at 23 ° C. and 0.045 g of Fe (DBP) 3 is brought into contact with 2 cm 3 of solution. The time required to obtain complete dissolution of the compound is then determined.

of iron.

  The results obtained and the conditions

  of dissolution are given in table 1.

  In view of these results, it can be seen that when the concentration of nitric acid is increased

  of the solution, the dissolution time is reduced.

Comparative example 1.

  In this example, the same procedure is followed as in Examples I to 3, but a solution containing only 1.5 mol / l is used.

  nitric acid in butyric acid.

  In these conditions, it is impossible

  to obtain the dissolution of the iron compound.

Comparative example 2.

  In this example, the same procedure is followed as in Examples I to 3, but the '

  solution contains only 0.4 mol / l dimethyldibu-

  tylmalonamide in butyric acid.

  Under these conditions, it is also impossible to obtain the dissolution of iron in a

reasonable time.

Examples 4 to 6.

  In these examples, the same procedure is followed as in Examples 1 to 3 to dissolve 0.071 g of Th (DBP) 4 using solutions of

  DMDBNA and nitric acid in butyric acid.

  The results obtained and the nitric acid and DMDBMA concentrations of the solutions are given.

in table 2.

  In view of this table, it can also be seen that the dissolution time decreases when the concentration of nitric acid in the solution is increased.

of dissolution.

Comparative example 3.

  In this example, the same procedure is followed as in Examples 4 to 6, but a solution containing only DMDBMA in butyric acid is used. Under these conditions, it is impossible to obtain the dissolution of the compound of

thorium.

2 6 4 1 4 0 4

Comparative free 4.

  In this example, the same procedure is followed as in Examples 4 to 6, but a solution containing only 1.5 mol / l of nitric acid in butyric acid is used. Under these conditions, it is also impossible to obtain the dissolution of the thorium compound.

Example 7.

  In this example, the same procedure is followed as in Examples 1 to 3 to dissolve 0.113 g of Nd (DBP) 3 using a solution of butyric acid containing 1.5 mol / l of nitric acid and

0.5mol / l DMDBNA.

  Under these conditions, the solution is obtained

  complete tion of the neodymium compound in 3 min.

Comparative example 5.

  In this example, the same procedure is followed as in Example 7, but a solution of butyric acid containing only

0.55 mol / l of DMDBMA.

  In these conditions, it is impossible

  to obtain the dissolution of the neodymium compound.

Comparative example 6.

  We follow the same procedure as in

  Example 7 but the butyric acid solution contains

  only holds 1.5mol / l of nitric acid.

  In these conditions, it is impossible

  to obtain the dissolution of the neodymium compound.

  The results and the conditions of dissolu-

  tion of Example 7 and Comparative Examples and 6 are grouped in Table 3.

Examples 8 to 11.

  In these examples, the same procedure is followed as in Examples I to 3 to dissolve

2 6 4 1 4 04

  0.045g of compound Fe (DBP) 3, but in this case, N, N-diethylacetamide is used as diluent

  (DEAAM) in Examples 8 and 9, namely N, N-dibutyl-

  formamide (DBFAM) in Examples 10 and 11.

  The nitric acid and DMDBMA concentrations of the solutions used and the times of

  dissolution are given in table 4.

  The results in Table 4 show that it is necessary to use higher nitric acid concentrations when the diluent

  is an amide instead of butyric acid.

  Indeed, under these conditions the molecule

  basic reacts with acid, and this results in

  this a reduction in the solubilizing power of the solvent which can be compensated for by the use of

  higher acid concentrations.

Examples 12 to 15.

  In these examples, the same procedure is followed as in Examples I to 3 to dissolve 0.045 g of Fe (DBP) 3 using a solution of DMDBMA and HNO3 in 2-octanol. The operation is also carried out at 23 C. The nitric acid and DMDBMA concentrations of the solutions used as well as the

  results obtained are given in table 5.

  In view of these results, it can be seen that it is also necessary to use higher nitric acid concentrations than in the

  examples I to 3 to quickly obtain dissolution.

Comparative free 7.

  In this example, the same procedure is followed as in Example 12, but the solution contains only DMDBMA. The DMDBMA concentration and the result obtained are given in darfs

table 5.

Comparative example 8.

  In this example, the same procedure is followed as in Example 12, but the solution

  contains only Nitric acid. The conditions

  dissolution and the result obtained are

  also given in Table 5.

  In view of the results of this table, it can be seen that it is impossible to obtain dissolution when the solution contains only acid.

nitric or only DMDBMA.

Example 16.

  In this example, a solution of butyric acid containing 0.45 mol / l of DMDBMA and lmol / l of nitric acid is used to decontaminate a mixer-decanter lined with Pu (DBP) 4. The apparatus is first rinsed with this solution, then rinsed again with nitric acid

  iN. We then send the two solutions to the incineration-

tion.

  At the end of the operation, a decontamination is obtained

  satisfactory mixing of the mixer-settler.

Example 17.

  In this example, a solution of butyric acid containing 0.45 mol / l of DMDBMA and lmol / l of nitric acid is used to decontaminate a distillation apparatus for solvent lined with Fe (DBP) 3. After rinsing the apparatus using this solution, a new rinsing is carried out with the diluent of the solvent distilled in this apparatus, for example TPH or hyfrane and the two rinsing solutions are sent to incineration .

  After these operations, we observe a

  satisfactory tamination of the distillation apparatus

lation.

2 6 4 1 4 0 4

26414O4

TABLE 1

  Dissolution conditions Time of Ex. Ex. C C C * dissolution HNO3 DMDBM4A Fe (DBP) (minutes) (mol.L-1) (mol.L-1) (mol.l-1 n

1 0.37 0.4 0.033 30 **

2 0.75 0.4 0.033 10

3 1.5 0.39 0.031 3

Ccmparat. 1 1.5 0

2 0 0.4

* after dissolution

** persistence of a slight clouding.

TABLE 2

  Dissolution conditions Time of Ex. C C C dissolution HNO3 DMDBMA Th (DBP) 4 (mol.l'1) (mol.l-1) (mol.L-'1 (minute

4 0.367 0.435 0.033 30

0.73 0.43 0.033 10

6 1.1 0.42 0.032 3

Comparat. 3 0 0.435 tu 4 1.5 0

TABLE 3

  Dissolution conditions Ex. Time C C C dissolution HNO3 DMDBMI4A Nd (DBP) 3 minutes (mol.L-1) (moL.L-1) (mol.1-1)

7 1.5 0.50 0.073 3

Comparat. 5 0 0.55

61.5 0

TABLE 4

Termination conditions

dissolved-

  Ex. CHNO3 CDMDBMA Thinner * CFe (DBP) tion mol.-1 mol.L-1 mol.l-1 minutes

8 1.47 0.46 DEAAM 0.034 25

9 2.94 0.43 DEAAM 0.034 10

1.47 0.4 DBFAM 0.034 30

11 2.94 0.38 DBFAM 0.034 10

  * DEAAM: N, N-diethyLacetamide; flash point: 700C

  DBFAM: N, N-dibutylformamide; flash point: 100 C.

TABLE 5

  Dissolution conditions Ex time C C C dissolution HNO3 DMD3a1A Fe (DBP) 3 minutes (mol.L-1) (mol.1-1) (mol.l-11

12 0.36 0.45 0.034 40 *

13 0.73 0.45 0.033 20

14 1.47 0.40 0.031 5

2.94 0.36 0.028 3

Comparat. 7 0 0.45

8 1.47 0

* Persistence of a slight disorder.

264 1,404

Claims (14)

  1. Solution for dissolving metal compounds comprising dibutylphosphate ions, characterized in that it comprises a diamide,   an organic diluent and an inorganic acid.   2. Solution according to claim 1,   characterized in that the diamide is a tetra-alkyl-   malonamide. 3. Solution according to claim 2, characterized in that the tetra-alkyl malonamide   is N, N'-dimethyl-N, N 'dibutyl-propanediamide.   4. Solution according to any one of   claims I to 3, characterized in that the   organic diluent is butyric acid.   5. Solution according to any one of   claims I to 3, characterized in that the   organic diluent is a diamide or an alcohol.   6. Solution according to claim 5,   characterized in that the diamide is N, N-diethyl-   acetamide or N, N-dibutylformamide.   7. Solution according to claim 5,   characterized in that the alcohol is octanol-2.   8. Solution according to any one of   Claims 1 to 7, characterized in that the acid inorganic is nitric acid.   9. Solution according to claim 1, characterized in that it is a solution of N, N'-dimethyl-N, N'-dibutyl-propanediamide and nitric acid in butyric acid, having an acid concentration nitric from 0, 1 to 4mol / L,   and a concentration of N, N'-dimethyl-N, N'-dibutyl-pro- panediamide from 0.1 to 1.5mol / l.   10. Solution according to any one of   Claims I to 8, characterized in that the   metallic compounds to be dissolved belong to the group of compounds of Pu (IV), U (IV), U (VI), La (III), Fe (III), Zr (IV), Th (IV) and rare earths in l 'state (III).   11. Device decontamination process   ges contaminated by precipitates of metallic compounds   ques containing dibutylphosphate ions, characterized in that the apparatus is rinsed by means of a dissolving solution according to any one of claims 1 to 9.   12. Method according to claim 11,   characterized in that the apparatus is then rinsed age with nitric acid.   13. The method of claim 11,   characterized in that the apparatus is then rinsed age with an organic thinner.   14. Method according to claim 13, characterized in that the organic diluent is an aliphatic hydrocarbon or a mixture of hydrocarbons aliphatic.